Sidewall thread bobbin

ABSTRACT

A sidewall bobbin having a core having two spaced-apart sidewalls carried and extending radially-outwardly from the core. At least one of the two side sidewalls includes a material having magnetic properties for interacting with a bobbin case having magnetically-attractive properties to apply drag to a thread being unwound from the bobbin and to retard overspin of the bobbin upon a reduction of the rate of removal of thread from the bobbin.

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION

This invention relates to a thread bobbins, and more particularly to magnetized bobbins that are pre-wound with sewing thread. More specifically, the present invention relates to pre-wound bobbins for use in sewing applications, such as embroidery stitching, and lock-stitch seaming and sewing in the garment and related industries. The novel bobbin provides improved uniformity of draw-off tension combined with reduced bobbin overspin. The magnetized pre-wound bobbins of this invention are also especially well suited for end-use sewing applications where automatic bobbin changing equipment is employed.

During lock stitch sewing, stitches are formed by a needle thread or threads, introduced from one side, interlacing with an underthread supplied from a bobbin on the other side. Typical lock stitch sewing results in strong seams with good strength and abrasion resistance, but has a disadvantage in the limited length of sewing that is possible before having to replace the underthread bobbin.

In this regard, the underthread is supplied or delivered from a bobbin that is located in a bobbin case beneath the sewing position. When performing lock stitch sewing, a commercial sewer will typically purchase pre-wound bobbins that are already wound with sewing thread in such a fashion that they can be placed inside the bobbin case for sewing. Pre-wound bobbins are conventionally supplied either with sidewalls (known in the art as “pre-wound sidewall bobbins”) or without sides (known in the art as “pre-wound sideless bobbins”).

Sidewall bobbins have a flange, or “sidewall” typically made from cardboard, plastic or paper. The thread is typically wound onto a flangeless core with the sidewalls (flanges) thereafter being attached to the core ends in a secondary operation. Alternatively, the thread may be wound onto a core with the sidewalls already attached. The former bobbin-winding technique allows the finished bobbin to be sized correctly by virtue of the pressure applied during the sidewall attachment process. The sidewalls prevent the yarn from looping under the bobbin or over the bobbin case post and subsequently breaking, control the thread draw-off tension, and act as a braking mechanism to reduce thread overspinning or backlash when sewing stops. In addition to these functions, bobbin sidewalls enhance proper performance on recently developed automated bobbin changing equipment.

Sideless bobbins have no sidewalls. Yarn is conventionally wound onto a cylindrical core in the production of pre-wound sideless bobbins. Unlike sidewall bobbins, the yarn wound on a sideless bobbin is tacked together to control the amount and uniformity of draw-off tension, to prevent the yarn from looping under or over the bobbin and subsequently breaking, and to control or reduce bobbin backlash or overspinning when sewing stops. A variety of techniques may be employed to tack the yarn on the sideless bobbins. Underthread supplied from a bobbin has a significant impact on seam quality as well as sewing productivity. The correct amount and uniformity of bobbin draw-off tension throughout the entire bobbin is important to achieve seam quality and performance.

The amount of draw-off tension is largely controlled by loosening or tightening a leaf spring located on the bobbin case so as to responsively decrease or increase, respectively, the spring's contact force against the thread. Draw-off tension that is not set correctly at the leaf spring or that changes during the sewing operation will cause loose stitches (on top or bottom) thus creating a defective seam. It is recognized in this art that the leaf spring is most desirably set so as to cause the thread to exhibit the least amount of draw-off tension consistent with high quality stitches. Lesser leaf spring pressure force on the thread, and thus a lesser amount of resulting draw-off tension, is known to cause less thread degradation due to frictional abrasion by the spring (and thereby also lessen the potential for thread lint and other debris to build-up under the spring). In addition, a lesser amount of spring pressure will not exacerbate tension non-uniformity caused inherently by thread surface irregularities.

The uniformity of draw-off tension as the bobbin is unwinding can be controlled or influenced by many factors. These factors include bobbin sidewalls, uniformity of yarn or thread diameter and thread friction, amount and uniformity of tack as the bobbin unwinds, and the ability of the tension spring to maintain uniform pressure or tension on the yarn as it passes through the bobbin case tension spring.

In addition to the amount and uniformity of the draw-off tension, controlling bobbin backlash or overspinning when sewing stops is another important factor in sewing quality and efficiency. Specifically, when the thread ceases to be pulled from the bobbin case, the bobbin in the bobbin case must not continue to spin and unravel to the point that the thread loops under the bobbin or over the bobbin case post that can snag and break when sewing is resumed. Even if the bobbin thread does not loop over or under the bobbin and snag after it overspins, the resulting slack created in the bobbin case can cause seam quality defects due to the subsequent tension variation once sewing is resumed.

Primary methods of controlling bobbin backlash or overspinning include use of the flanges on sidewall bobbins as well as the amount of tack on sideless bobbins. For example, the flanges of a sidewall bobbin act as a braking mechanism to help reduce the amount of backlash or overspinning when sewing stops. In addition, the flanges of a sidewall bobbin prevent the thread from looping over or under the bobbin. Assuming the proper amount and uniformity of draw-off tension, it is generally known in the art that the least amount of bobbin overspin will produce a more consistent sewn seam due to less tension variations and reduce the possibility of bobbin thread breaks.

Tension control is a principal factor in reducing overspin, and the prior art, U.S. Pat. No. 6,257,512, recognizes the use of a magnetized core in a sideless bobbin as a means of controlling tension and overspin. The magnetic core is intended to generate a magnetic attraction between the core and ferro metallic bobbin case and the bobbin case post. However, the placement of the magnetized element radially-inwardly reduces the evenness of the magnetic force by concentrating it in a relatively small area with a very short radius. The present invention provides the benefits of a sidewall bobbin with excellent tension and overspin control by providing a sidewall that exhibits magnetic properties across a relatively wide surface area along a relatively long radius, so as to provide even tension control by interaction with the ferromagnetic bobbin case within which the bobbin is contained.

SUMMARY OF THE INVENTION

Therefore, it is an object of the invention to provide a sidewall bobbin that has a sidewall exhibiting magnetic properties.

It is another object of the invention to provide a sidewall bobbin that has a magnetic sidewall that magnetically interacts with a ferromagnetic bobbin case within which the bobbin carried.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the objects of the invention have been set forth above. Other objects and advantages of the invention will appear as the description of the invention proceeds when taken in conjunction with the following drawings, in which:

FIG. 1 is a perspective view of a sidewall bobbin according to one embodiment of the invention; and

FIG. 2 is a cross-sectional view of a sidewall bobbin according to one embodiment of the invention positioned in a conventional bobbin case.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE

Referring now the drawings, a sidewall bobbin is shown and broadly indicated a reference numeral 10. The bobbin 10 has a core 12, a conventional sidewall 14 made of, for example, paper carton material, fiberboard, plastic, or the like, and a sidewall 16 that includes a material that exhibits magnetic properties. Alternatively, both sidewalls 14 and 16 may be include a material that exhibits magnetic properties (not shown), as explained and described below.

While the sidewall 16 can be formed of magnetized metal, the sidewall 16 is preferably fabricated of a thermoplastic resin containing a dispersion of magnetized particles. The sidewall 16 is preferably formed of a thermoplastic resin that serves as a carrier matrix, such as nylon, polyacetal, polyester, polyolefin or the like. Thermoset resins may also be used as the carrier matrix. The thermoplastic resin may itself include other ingredients and/or components that are typically included with conventional thermoplastic resins such as, for example, stabilizers, antioxidants, lubricants, reinforcing agents, mold-release agents, coloring agents, inorganic and/or organic fillers and the like. These additional components may be used in any quantities provided that the magnetic properties of the bobbin sidewall 16 are not significantly adversely affected. The resin will typically be formed as a sheet or film and subsequently die-cut to form the annular sidewall 16, that is then applied to the core 12 in a conventional manner.

The magnetized particles may include ferromagnetic particles such as elemental iron particles, and/or ferrite (ceramic) powder based on barium or strontium carbonate (general composition BaFe₂O₃ or SrFe₂O₃). Alternatively or in addition to the ferrite particles, the particles can be formed of other magnetic materials such as rare earth magnetic materials (e.g., neodymium iron boron (Nd₂Fe.sub₁₄B) or samarium cobalt (SmCo₅, Sm₂ Co₇)), or aluminum-nickel-cobalt (Alnico) alloys.

The material from which the sidewall 16 is formed are preferably anisotropic, i.e., having a preferred direction of magnetic orientation, so that the magnetic characteristics are optimum in a direction opposite the direction of rotation of the bobbin 10 during use. In this manner, a magnetically-induced “drag” is imposed on the bobbin. The thickness of the sidewall 16 is dependent on the strength of the magnetic material being used, consistent with the necessity to provide a sidewall 16 that is stiff enough to provide support to the thread on the bobbin 10. The desired thickness is on the order of less than 1 mm. Resins impregnated with, for example, samarium cobalt, can be paper thin and still exhibit excellent overspin characteristics. This will increase the amount of thread capacity of the bobbin 10.

Alternatively, a film (not shown) having magnetic properties can be bonded to the outer face of a sidewall constructed of conventional materials, as described above, a liquid or paste having magnetic properties can be applied to the outer face of a sidewall constructed of conventional materials. Similarly, the entire sidewall need not be comprised of or exhibit magnetic properties. The principal factor is the provision of a material having sufficient magnetic properties to exercise proper tension and overspin control. The particular magnetic material and its mode of application to the bobbin depends on the operating characteristics of the sewing operation to which it will be applied.

As shown in FIG. 2, the sidewall 16 of the bobbin 10 is positioned in a bobbin case 20. The bobbin case 20 has magnetically-attractive properties, either because the bobbin case 20 itself is made of ferrous materials, such as steel, or is provided with a magnetically-attracted cover or insert. As thread is withdrawn from the bobbin 10, rotation of the bobbin 10 is subjected to drag-induced tension provided by the sidewall 16 rotating in close proximity to the bobbin case 20. Similarly, when sewing ceases or slows, the bobbin 10 is subjected to sufficient drag to prevent the bobbin 10 from continuing to rotate at a rate faster than the take-off rate of the thread.

An improved sidewall bobbin is described above. Various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description of the preferred embodiment of the invention and best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation, the invention being defined by the claims. 

1. A sidewall bobbin comprising a core having two spaced-apart sidewalls carried and extending radially-outwardly from the core, at least one of the two side sidewalls comprising a material having anisotropic magnetic properties having a preferred direction of magnetic orientation opposite an unwinding direction of rotation of the sidewall bobbin during use for interacting with a bobbin case having magnetically-attractive properties to apply drag to a thread being unwound from the bobbin and to retard overspin of the bobbin upon a reduction of the rate of removal of thread from the bobbin, such that the anisotropic magnetic properties retard rotation of the sidewall bobbin in the unwinding direction and do not retard rotation of the sidewall bobbin in the winding direction.
 2. A sidewall bobbin according to claim 1, wherein one of the two sidewalls comprises a conventional sidewall material, and the other of the two sidewalls comprises a material that exhibits magnetic properties
 3. A sidewall bobbin according to claim 1, wherein the at least one of the two sidewalls comprises a material selected from the group consisting of ferromagnetic particles.
 4. A sidewall bobbin according to claim 1, wherein the at least one of the two sidewalls comprises a magnetic material selected from the group consisting of elemental iron particles, ferrite powder based on barium or strontium carbonate, rare earth magnetic materials or aluminum-nickel-cobalt alloys.
 5. A sidewall bobbin according to claim 4, wherein the magnetic material is in the form of particles dispersed in a resin.
 6. A sidewall bobbin according to claim 1, wherein the at least one of the two sidewalls comprises a thermoplastic resin containing a dispersion of magnetized particles.
 7. A sidewall bobbin according to claim 1, wherein the material having magnetic properties comprises particles dispersed in a carrier matrix.
 8. A sidewall bobbin according to claim 1, wherein the material having magnetic properties comprises a film applied to a sidewall substrate.
 9. A sidewall bobbin according to claim 1, wherein the material having magnetic properties comprises a liquid or paste applied to a sidewall substrate.
 10. A sidewall bobbin comprising a core having at least one sidewall carried and extending radially-outwardly from the core, and comprising a material having anisotropic magnetic properties having a preferred direction of magnetic orientation opposite an unwinding direction of rotation of the bobbin during use for interacting with a bobbin case having magnetically-attractive properties to apply drag to a thread being unwound from the bobbin and to retard overspin of the bobbin upon a reduction of the rate of removal of thread from the bobbin, such that the anisotropic magnetic properties retard rotation of the bobbin in the unwinding direction and do not retard rotation of the bobbin in the winding direction.
 11. A sidewall bobbin according to claim 10, wherein the sidewall comprises a material selected from the group consisting of ferromagnetic particles.
 12. A sidewall bobbin according to claim 10, wherein the at least one sidewall comprises a magnetic material selected from the group consisting of elemental iron particles, ferrite powder based on barium or strontium carbonate, rare earth magnetic materials or aluminum-nickel-cobalt alloys.
 13. A sidewall bobbin according to claim 4, wherein the magnetic material is in the form of particles dispersed in a resin. 